How can I export an object to multiple scales at once?
When you say export, I expect you need it in a non-blender format, say for 3D printing. Most export options have a scale parameter that can easily save each export in a different size.

import bpy

ring_sizes = [0.8,0.9,1.0,1.1,1.2,1.3,1.4,1.5,1.6]

for s in ring_sizes:
    bpy.ops.export_mesh.ply(filepath="Ring_"+str(s)+".ply", global_scale=s)